The invention relates to a fuel injection pump for internal combustion engines provided with a cam drive mechanism which causes a conveying motion of at least one pump piston. A fuel injection pump of the type to which the invention is directed is shown in U.S. Pat. No. 3,906,916. The cam drive mechanism further comprises a roller ring which is rotatable by means of a device which operates in dependence on rpm for the purpose of adjusting the onset of injection. In a conventional fuel injection pump, the instant of onset of injection of the hydraulically operating injection timing mechanism is set to "early" during start-up. At a higher speed, the onset of injection is then automatically shifted to "later" and then is readjusted to "early" during an increase in the number of revolutions. In another conventional device of this type, the starting position of the operating piston of the injection timing mechanism is shifted to "early " by means of a stop, as long as the engine is cold. While, in the former case, a relatively expensive hydraulic control must be provided, the second case involves the problem of sealing the stop which projects into the pressure chamber of the servo piston.